SPC MD 1964


MD 1964 Image

Mesoscale Discussion 1964
NWS Storm Prediction Center Norman OK
0102 PM CDT Thu Sep 12 2019

Areas affected...southern PA and portions of the Mid-Atlantic

Concerning...Severe potential...Watch possible 

Valid 121802Z - 122000Z

Probability of Watch Issuance...40 percent

SUMMARY...Thunderstorms are expected to develop over the next 1-2
hours and southeast across the Mid-Atlantic/Chesapeake Bay area
through this evening. Strong wind gusts will be the main concern
with this activity, and a watch may be needed this afternoon.

DISCUSSION...Strong heating ahead of a southward sagging cold front
has resulted in temperatures climbing into the mid 80s to low 90s
this afternoon. A very moist airmass with dewpoints generally in the
upper 60s to low 70s is in place, resulting in MLCAPE values around
1000-2000 J/kg. Upper level forcing is weak across the region, with
convective development mainly due to heating along the front and
weak confluence along a surface trough further south in the
Chesapeake Bay vicinity. Effective shear will remain modest, around
25-30 kt, but in the presence of moderate instability this should be
sufficient for sustained, organized updrafts. The main concern this
afternoon into this evening will be strong wind gusts. Low level
thermodynamic profiles show inverted-v signatures while 17z
mesoanalysis indicated very steep low level lapse rates. Storms may
organize into a forward propagating cluster/bowing segment through
outflow interactions/storm mergers, increasing damaging wind
potential if this occurs, though convective coverage may remain too
isolated in the absence of stronger ascent. Thunderstorms will
spread southeast toward the I-95 corridor and mid-Atlantic coast
through this evening. Trends will be monitored and a watch may be
needed this afternoon.

Further south toward southeast VA into northeast NC, more isolated
pulse-type storms are possible where low level convergence along the
surface trough more apparent. Weak deep layer flow and a lack of
stronger ascent should limit organized convection, through a couple
of strong gusts can not be ruled out.

..Leitman/Hart.. 09/12/2019

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   41467752 40457475 39477401 38567464 36687529 36607579
            36817652 37387725 39287805 40307838 40877826 41207813

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